Abstract:

A method for making a carbon nanotube composite includes: (a) providing at
least one carbon nanotube film and at least one polymer film; (b) forming
a carbon nanotube film structure with the carbon nanotube film on a
surface of the polymer film to obtain a carbon nanotube composite
preform; (c) pre-combining the carbon nanotube composite preform to
obtain a treated carbon nanotube composite preform; and (d) heating and
pressing at least one treated carbon nanotube composite preform to
achieve a carbon nanotube composite.

Claims:

1. A method for making a carbon nanotube composite, the method comprising
the following steps of:(a) providing at least one carbon nanotube film
and at least one polymer film;(b) forming a carbon nanotube film
structure with the one or more carbon nanotube films; locating the carbon
nanotube film structure on a surface of the polymer film to obtain a
carbon nanotube composite preform;(c) pre-combining the carbon nanotube
composite preform to obtain a treated carbon nanotube composite preform;
and(d) heating and pressing at least one treated carbon nanotube
composite preform to achieve a carbon nanotube composite.

2. The method as claimed in claim 1, wherein the method further comprises
the step of (e) fabricating at least one carbon nanotube film,
fabricating the at least one carbon nanotube film comprises the following
substeps of:(e1) providing a substrate with an array of carbon nanotubes
formed thereon;(e2) selecting a plurality of carbon nanotube segments
from the array of carbon nanotubes; and(e3) pulling the carbon nanotube
segments at an even/uniform speed to achieve a uniform carbon nanotube
film.

3. The method as claimed in claim 1, wherein step (b) further comprises
placing the at least one carbon nanotube film on a surface of the polymer
film directly.

4. The method as claimed in claim 3, wherein at least two carbon nanotube
films are placed side-by-side or at least two carbon nanotube films are
stacked.

5. The method as claimed in claim 4, wherein each carbon nanotube film
comprises a plurality of carbon nanotubes oriented along the same
direction, the orientation of the carbon nanotubes in any two adjacent
carbon nanotube films form an angle α, and
0.ltoreq.α≦90.degree..

6. The method as claimed in claim 1, wherein step (b) comprises the
following substeps of:(b1') providing a supporter;(b2') attaching at
least one carbon nanotube film onto the supporter and removing the
unwanted carbon nanotube film;(b3') removing the supporter to obtain the
carbon nanotube film structure; and(b4') providing at least one polymer
film, and stacking the polymer film and the carbon nanotube film
structure.

7. The method as claimed in claim 6, wherein the step of attaching at
least one carbon nanotube film onto the supporter comprises placing at
least two carbon nanotube films side-by-side or stacking at least two
carbon nanotube films on a surface of the supporter.

8. The method as claimed in claim 7, wherein each carbon nanotube film
comprises a plurality of carbon nanotubes oriented along the same
direction, and the orientation of the carbon nanotubes in any two
adjacent stacked carbon nanotube films form an angle α, and
0.ltoreq.α≦90.degree..

9. The method as claimed in claim 1, further comprising a step of treating
the carbon nanotube film structure with an organic solvent after the step
(b).

10. The method as claimed in claim 9, wherein the step of treating the
carbon nanotube film structure with an organic solvent is performed by
applying the organic solvent onto the surface of the carbon nanotube film
structure or dipping the carbon nanotube film structure in an organic
solvent.

11. The method as claimed in claim 1, wherein the thickness of the polymer
film approximately ranges from 2 micrometers to 2 millimeters.

12. The method as claimed in claim 1, wherein the step (c) is carried out
by a hot-pressing apparatus, and the hot-pressing apparatus is selected
from the group consisting of double roll device, flat hot-pressing
shaper, hot press, flat vulcanizer, and oven.

13. The method as claimed in claim 1, wherein the step (c) is carried out
by passing the carbon nanotube composite preform through a double roll
device, and the velocity of passing the carbon nanotube composite preform
through the double roll device approximately ranges from 1 millimeter per
minute to 10 meters per minute.

14. The method as claimed in claim 13, wherein the step (c) is repeated.

15. The method as claimed in claim 1, wherein the step (c) is carried out
at a temperature above the softening temperature of the polymer film.

16. The method as claimed in claim 1, wherein the step (d) comprises the
following substeps of:(d1) placing the pre-combined carbon nanotube
composite preform into a hot-pressing apparatus;(d2) heating and pressing
the pre-combined carbon nanotube composite preform, and keeping the
situation for a period of time; and(d3) cooling down and demoulding the
carbon nanotube composite preform to achieve the carbon nanotube
composite.

17. The method as claimed in claim 16, wherein the step (d2) comprises the
following substeps of: (d21) heating the pre-combined carbon nanotube
composite preform up to a temperature above the melting point of the
polymer film; and (d22) pressing the carbon nanotube composite preform
and keeping the situation for a period of time.

18. The method as claimed in claim 16, wherein the step (d2) comprises the
following substeps of: (d21') pressing the carbon nanotube composite
preform; and (d22') heating the pre-combined carbon nanotube composite
preform up to the melting point of the polymer film.

19. The method as claimed in claim 16, wherein the step (d2) is performed
by heating the pre-combined carbon nanotube composite preform up to the
melting point of the polymer film and pressing the carbon nanotube
composite preform simultaneously.

20. The method as claimed in claim 16, wherein the pressure of pressing
the pre-combined carbon nanotube composite preform is lower than 100 Mpa,
the period of time of keeping the pressure on the carbon nanotube
composite preform is shorter than 2 hours, and the temperature of
demoulding is below 60.degree. C.

Description:

RELATED APPLICATIONS

[0001]This application is related to commonly-assigned applications
entitled, "METHOD FOR MAKING CARBON NANOTUBE BASED COMPOSITE", filed
(Atty. Docket No. US17642); and "CARBON-NANOTUBE-BASED COMPOSITE MATERIAL
AND METHOD FOR MAKING THE SAME", filed (Atty. Docket No. US17608). The
disclosures of the above-identified applications are incorporated herein
by reference.

BACKGROUND

[0002]1. Field of the Invention

[0003]The present invention relates to methods for making composites and,
particularly, to a method for making a carbon nanotube composite.

[0004]2. Discussion of Related Art

[0005]Carbon nanotubes (CNTs) are novel carbonaceous materials and have
received a great deal of interest since the early 1990s. Carbon nanotubes
have interesting and potentially useful heat conductive, electrical, and
mechanical properties. Due to these and other properties, it becomes an
important application direction for CNTs to be used as fillers in
composite materials.

[0006]A conventional method for making a carbon nanotube composite
includes the following steps of: (a) functionalizing the carbon
nanotubes; (b) dispersing the functionalized carbon nanotubes into a
thermoplastic polymer solution to obtain a mixture; (c) spraying or
dipping the mixture on a substrate to form a layer; and (d) volatilizing
the solvent in the layer to achieve a carbon nanotube composite.

[0007]However, some drawbacks arise from the conventional method for
making carbon nanotube composite. Firstly, it is difficult to uniformly
disperse the carbon nanotubes into thermoplastic polymer solution.
Secondly, the process of functionalizing the carbon nanotubes will damage
the integrality of the carbon nanotubes. Thirdly, the carbon nanotubes
distribute in the polymer disorderly.

[0008]What is needed, therefore, is a method for making carbon nanotube
composite that can orderly distribute the carbon nanotubes into the
polymer matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]Many aspects of the present method for making a carbon nanotube
composite can be better understood with references to the following
drawings. The components in the drawings are not necessarily drawn to
scale, the emphasis instead being placed upon clearly illustrating the
principles of the present method for making the carbon nanotube
composite.

[0010]FIG. 1 is a flow chart of a method for making a carbon nanotube
composite in accordance with the present embodiment;

[0011]FIG. 2 is a schematic view of the carbon nanotube composite preform
formed by the method of FIG. 1;

[0012]FIG. 3 is a schematic view of a carbon nanotube film structure
formed by the method of FIG. 1;

[0013]FIG. 4 is a schematic view of an apparatus used for pre-combining
the carbon nanotube composite preform of FIG. 1;

[0014]FIG. 5 is a schematic view of an apparatus used for heating and
pressing the carbon nanotube composite preform of FIG. 1;

[0015]FIG. 6 is a schematic view of the carbon nanotube composite formed
by the method of FIG. 1.

[0016]Corresponding reference characters indicate corresponding parts
throughout the several views. The exemplifications set out herein
illustrate at least one embodiment of the method for making the carbon
nanotube composite, in at least one form, and such exemplifications are
not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0017]References will now be made to the drawings to describe, in detail,
embodiments of the method for making the carbon nanotube composite.

[0018]Referring to FIG. 1, a method for making a carbon nanotube composite
includes the following steps of: (a) providing at least one carbon
nanotube film and at least one polymer film; (b) forming a carbon
nanotube film structure with the carbon nanotube films on a surface of
the polymer film to obtain a carbon nanotube composite preform; (c)
pre-combining the carbon nanotube composite preform to obtain a treated
carbon nanotube composite preform; and (d) heating and pressing at least
one treated carbon nanotube composite preform to achieve a carbon
nanotube composite.

[0019]The step (a) includes a step of (e) fabricating at least one carbon
nanotube film. The step (e) includes the following substeps of: (e1)
providing a substrate with a super-aligned array of carbon nanotubes
formed thereon; (e2) selecting a plurality of carbon nanotubes ("carbon
nanotube segments") having a predetermined width from the super-aligned
array of carbon nanotubes; and (e3) pulling out a carbon nanotube film
from the array of carbon nanotubes via a pulling tool (e.g., adhesive
tape or another tool allowing multiple carbon nanotubes to be gripped and
pulled simultaneously), and achieving a carbon nanotube film.

[0020]In step (e1), a given super-aligned array of carbon nanotubes can be
formed by the substeps of: (e11) providing a substantially flat and
smooth substrate; (e12) forming a catalyst layer on the substrate; (e13)
annealing the substrate with the catalyst layer in air at a temperature
approximately ranging from 700° C. to 900° C. for about 30
to 90 minutes; (e14) heating the substrate with the catalyst layer to a
temperature approximately ranging from 500° C. to 740° C.
in a furnace with a protective gas therein; and (e15) supplying a carbon
source gas to the furnace for about 5 to 30 minutes and growing the
super-aligned array of carbon nanotubes on the substrate.

[0021]In step (e11), the substrate can be a P-type silicon wafer, an
N-type silicon wafer, or a silicon wafer with a film of silicon dioxide
thereon. A 4-inch P-type silicon wafer is used as the substrate.

[0022]In step (e12), the catalyst can be made of iron (Fe), cobalt (Co),
nickel (Ni), or any alloy thereof.

[0023]In step (e14), the protective gas can be made up of at least one of
nitrogen (N2), ammonia (NH3), and a noble gas. In step (a5),
the carbon source gas can be a hydrocarbon gas, such as ethylene
(C2H4), methane (CH4), acetylene (C2H2), ethane
(C2H6), or any combination thereof.

[0024]The super-aligned array of carbon nanotubes can be approximately 200
to 400 micrometers in height, with the super-aligned array including a
plurality of carbon nanotubes parallel to each other and approximately
perpendicular to the substrate. The carbon nanotubes in the carbon
nanotube film can be selected from the group consisting of single-walled
carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon
nanotubes. A diameter of each single-walled carbon nanotube approximately
ranges from 0.5 to 50 nanometers. A diameter of each double-walled carbon
nanotube approximately ranges from 1 to 50 nanometers. A diameter of each
multi-walled carbon nanotube approximately ranges from 1.5 to 50
nanometers.

[0025]The super-aligned array of carbon nanotubes formed under the above
conditions is essentially free of impurities, such as carbonaceous or
residual catalyst particles. The carbon nanotubes in the super-aligned
array are closely packed together by van der Waals attractive force.

[0026]In step (e2), the carbon nanotube segments having a predetermined
width can be selected by using an adhesive tape, such as the tool, to
contact the super-aligned array. In step (e3), the pulling direction is
substantially perpendicular to the growing direction of the super-aligned
array of carbon nanotubes and the carbon nanotube segments are pulled at
an even/uniform speed.

[0027]More specifically, during the pulling process, as the initial carbon
nanotube segments are drawn out, other carbon nanotube segments are also
drawn out end-to-end due to van der Waals attractive force between ends
of adjacent segments. This process of drawing ensures that a continuous
and uniform carbon nanotube film having a predetermined width can be
formed. The carbon nanotube film includes a plurality of carbon nanotube
segments containing a plurality of carbon nanotubes. The carbon nanotubes
in the carbon nanotube film are all substantially parallel to the
pulling/drawing direction of the carbon nanotube film, and the carbon
nanotube film produced in such manner can be selectively formed to have a
predetermined width. The carbon nanotube film formed by the
pulling/drawing method has a superior uniformity of thickness and
conductivity over a typically disordered carbon nanotube film.
Furthermore, the pulling/drawing method is simple, fast, and suitable for
industrial applications.

[0028]The width of the carbon nanotube film depends on a size of the
carbon nanotube array. The length of the carbon nanotube film can be
arbitrarily set as desired. In one useful embodiment, when the substrate
is a 4-inch P-type silicon wafer, the width of the carbon nanotube film
approximately ranges from 0.01 to 10 centimeters, while the thickness of
the carbon nanotube film approximately ranges from 0.5 nanometers to 100
micrometers. The carbon nanotubes in the carbon nanotube film can be
selected from the group consisting of single-walled carbon nanotubes,
double-walled carbon nanotubes, and multi-walled carbon nanotubes.
Diameters of the single-walled carbon nanotubes approximately range from
0.5 to 50 nanometers. Diameters of the double-walled carbon nanotubes
approximately range from 1 to 50 nanometers. Diameters of the
multi-walled carbon nanotubes approximately range from 1.5 to 50
nanometers.

[0030]Referring to FIG. 2, in step (b), the carbon nanotube composite
preform 10 can be made by the methods of: laying at least one carbon
nanotube film directly on a surface of the first polymer film 14 to
obtain the carbon nanotube composite preform 10. Also, the carbon
nanotube composite preform 10 can be made by the methods of: stacking
several carbon nanotube films to form a self-supporting carbon nanotube
film structure 12, and then placing the carbon nanotube film structure 12
on a surface of the first polymer film 14 to obtain the carbon nanotube
composite preform 10.

[0031]The method of laying at least one carbon nanotube film directly on a
surface of the first polymer film 14 to obtain the carbon nanotube
composite preform 10 includes the following steps of: (b1) providing a
first polymer film 14; (b2) laying at least one carbon nanotube film on a
surface of the first polymer film 14; (b3) removing unwanted carbon
nanotube film to form a carbon nanotube film structure 12 on a surface of
the first polymer film 14, thereby obtaining a carbon nanotube composite
preform 10.

[0032]In the present embodiment, the carbon nanotube composite preform 10
can be obtained by contactingly placing at least two carbon nanotube
films side-by-side and/or stacking at least two carbon nanotube films to
form a carbon nanotube film structure 12 on the surface of the first
polymer film 14. Coplanar carbon nanotube films located side-by-side form
a carbon nanotube layer. Therefore, the carbon nanotube film structure 12
includes one carbon nanotube layer or at least two carbon nanotube layers
stacked with one another. The extending direction of the carbon nanotubes
in any two adjacent carbon nanotube layers form an angle α, and
0≦α≦90°. The angle α is 90° in
the present embodiment. The angles can also vary between different
adjacent pairs of carbon nanotube films.

[0033]Furthermore, the second polymer film 16 can be placed on the carbon
nanotube film structure 12 to form a carbon nanotube composite preform 10
of sandwich structure as seen in FIG. 2. The sandwich structure could
prevent the carbon nanotube in the carbon nanotube film structure 12 from
being adhered to the pressing device in following steps. It is to be
understood that a multilayer carbon nanotube composite preform 10 can be
made via stacking several polymer films and carbon nanotube films
structure in turn.

[0034]The method of stacking the carbon nanotube films to form a
self-supporting carbon nanotube film structure 12, and then placing the
carbon nanotube film structure 12 on a surface of the first polymer film
14 to obtain the carbon nanotube composite preform 10 includes the
following steps of: (b1') providing a supporter; (b2') attaching at least
one carbon nanotube film onto the supporter and removing the unwanted
carbon nanotube film; (b3') removing the supporter to obtain the carbon
nanotube film structure 12; and (b4') providing at least one first
polymer film 14, and stacking the first polymer film 14 and the carbon
nanotube film structure 12 to obtain a carbon nanotube composite preform
10.

[0035]The supporter can be a substrate or a frame. Because the carbon
nanotubes in the super-aligned carbon nanotube array have a high purity
and a high specific surface area, the carbon nanotube film is adherent in
nature. As such, the carbon nanotube film can be directly adhered to the
substrate or frame. The unwanted carbon nanotube film can be cut off via
a knife or a laser beam.

[0036]The area and shape of the supporter can be chosen according to
user-specific needs. When the width of the supporter is larger than the
width of carbon nanotube film, the carbon nanotube film structure 12 can
be obtained by contactingly placing at least two carbon nanotube films
side-by-side and/or stacking at least two carbon nanotube films on the
surface of the supporter. At least two coplanar carbon nanotube films
contactingly located side-by-side form a carbon nanotube layer.
Therefore, the carbon nanotube film structure 12 can include, one or more
stacked carbon nanotube films, one carbon nanotube layer or at least two
stacked carbon nanotube layers. The desired size will determine the
configuration of the carbon nanotube film structure 12. The extending
direction of the carbon nanotubes in any two adjacent carbon nanotube
layers form an angle α, and 0≦α≦90°. The
angle α is 90° in the present embodiment. Referring to FIG.
3, in the present embodiment, the carbon nanotube film structure 12 is
made by stacking four carbon nanotube layers 122. The extending direction
of the carbon nanotubes in any two adjacent carbon nanotube layers 122 is
perpendicular in the present embodiment.

[0037]A step of treating the carbon nanotube film structure 12 with an
organic solvent can be optionally provided after step (b). The organic
solvent is volatilizable and can be selected from the group consisting of
ethanol, methanol, acetone, dichloroethane, chloroform, and any
appropriate mixture thereof. In the present embodiment, the organic
solvent is ethanol. Specifically, the carbon nanotube film structure 12
can be treated by applying organic solvent onto the surface of the carbon
nanotube film structure 12 or dipping the entire carbon nanotube film
structure 12 in an organic solvent. During the surface treatment,
adjacent carbon nanotubes bundle up into numerous successive carbon
nanotube strings. The specific surface area and sticky property of the
treated carbon nanotube strings is reduced, thereby improving the
strength and toughness of the carbon nanotube film structure.

[0038]Referring to FIG. 4, the step (c) of pre-combining the carbon
nanotube composite preform 10 can be carried out via a hot-pressing
apparatus selected from the group consisting of double roll device 20,
flat hot-pressing shaper, hot press, flat vulcanizer, and oven. The
purpose of pre-combining is to evacuate the air in the carbon nanotube
composite preform 10 and soften the polymer film. The soft polymer film
could connect with the carbon nanotubes in the carbon nanotube film
structure 12 closely.

[0039]In the present embodiment, the step (c) is carried out via a double
roll device 20. The double roll device 20 includes two metal rollers 22
and a heating device. The carbon nanotube composite preform 10 is passed
through the hot double roll device 20 slowly with a velocity ranged from
approximate 1 millimeter per minute to 10 meters per minute. The
temperature of the double roll device 20 is higher than the softening
temperature of the polymer film so as to soften the polymer film to
connect with the carbon nanotubes in the carbon nanotube film structure
12 closely. Therefore, the temperature of the double roll device 20
varies with the softening temperature of the polymer film. In order to
evacuate the air in the carbon nanotube composite preform 10 entirely,
the step (c) can be repeated many times. It is to be understood that the
process of pre-combining can also be carried out in a vacuum so as to
evacuate the air in the carbon nanotube composite preform 10 more
effectively.

[0040]Referring to FIG. 5, in the step (d), the process of heating and
pressing the treated carbon nanotube composite preform 50 is carried out
via a hot-pressing apparatus. During the step (d), the polymer film
becomes molten and infiltrates micropores of the carbon nanotube film
structure 12.

[0041]The step (d) includes following substeps of: (d1) placing the
treated carbon nanotube composite preform 50 into a hot-pressing
apparatus; (d2) heating and pressing the treated carbon nanotube
composite preform 50 for a pre-determined period of time; and (d3)
cooling down and demoulding the treated carbon nanotube composite preform
50 to achieve the carbon nanotube composite.

[0042]In the step (d1), the hot-pressing apparatus can be selected from
the group consisting of hot press, flat hot-pressing shaper, flat
vulcanizer, and oven. Referring to FIG. 5, in the present embodiment, the
hot-pressing apparatus is a hot press 30. The hot press 30 includes a
pressing device, a heating device and a mold 32. The mold 32 includes an
upper male portion 34 and a bottom female portion 36. An optional step of
coating releasing agent on an inner surface of mould 32 can be provided
before placing the treated carbon nanotube composite preform 50 therein.
The releasing agent will facilitate the process of demolding in following
step. The materials of the releasing agent various with the materials of
the polymer film. The releasing agent can be selected from the group
consisting of silicon releasing agent, wax releasing agent, and siloxane
releasing agent.

[0043]The step (d2) could include the following substeps of: (d21) heating
the treated carbon nanotube composite preform 50 up to a temperature
above the melting point of the polymer film 14; and (d22) pressing the
treated carbon nanotube composite preform 50 for a period of time long
enough to melt the polymer film entirely and allow infiltration of the
polymer materials into the micropores of the carbon nanotube film
structure 12. These steps can be performed individually as well as
simultaneously.

[0044]The step (d2) could include the following substeps of: (d21')
pressing the treated carbon nanotube composite preform 50; and (d22')
heating the treated carbon nanotube composite preform 50 up to the
melting point of the polymer film for a period of time long enough to
melt the polymer film entirely allowing infiltration of the polymer
materials into the micropores of the carbon nanotube film structure 12.

[0045]The step (d2) can be carried out by heating the treated carbon
nanotube composite preform 50 up to the melting point of the polymer film
and pressing the treated carbon nanotube composite preform 50 at the same
time until the polymer film melts entirely and the polymer materials
infiltrate into the micropores of the carbon nanotube film structure 12.

[0046]In the step (d2), the heating temperature varies with the melting
temperature of the polymer film. The heating temperature is above the
melting temperature of the polymer film so as to melt the polymer film
entirely and infiltrate the polymer materials into the micropores of the
carbon nanotube film structure 12. The pressure is lower than 100 Mpa.
The period of time for keeping the pressure on the treated carbon
nanotube composite preform 50 is shorter than 2 hours. It is to be
understood that several stacked treated carbon nanotube composite
preforms 50 can be heated and pressed together.

[0047]In the step (d3), the treated carbon nanotube composite preform 50
can be actively or passively cooled. In the present embodiment, the
demoulding is carried out at a temperature below 60° C.

[0048]Referring to FIG. 6, a carbon nanotube composite 40 is fabricated in
the present embodiment. The carbon nanotube composite 40 includes a
polymer matrix 46 and a plurality of carbon nanotubes orderly distributed
in the polymer matrix 46. The carbon nanotubes distribute in the polymer
matrix 46 in form of carbon nanotube film structure 42.

[0049]It is also to be understood that the description and the claims may
include some indication in reference to certain steps. However, the
indication used is applied for identification purposes only, and the
identification should not be viewed as a suggestion as to the order of
the steps.

[0050]It is to be understood that the above-described embodiments are
intended to illustrate rather than limit the invention. Variations may be
made to the embodiments without departing from the spirit of the
invention as claimed. The above-described embodiments illustrate the
scope of the invention but do not restrict the scope of the invention.